DIRECT RADIOIMMUNOASSAY OF PROGESTERONE IN BOVINE PLASMA USING DANAZOL -ALPHA-2,4-PREGNADIEN-20-YNO(2,3-D)ISOXAZOL-17-OL) AS A DISPLACING AGENT

The majority of progesterone in plasma is bound to cortisol-binding gl obulin and albumin carrier proteins. In the determination of plasma pr ogesterone concentration by radioimmunoassay (RIA), it is necessary to remove these carrier proteins or displace the hormone from them. In t he present study, we have examined the suitability of danazol alpha-2, 4-pregnadien-20-yno(2,3-d)isaxazol-17-ol), a synthetic steroid, to dis place progesterone from plasma proteins in a direct RIA of bovine plas ma. Accordingly, the progesterone content of bovine plasma samples was measured with a RIA using danazol as a displacing agent (direct RIA) and compared with results obtained with a RIA incorporating a prelimin ary solvent extraction step (extraction RIA). Danazol did not alter th e standard curve for progesterone. Sensitivity (ED(80)) of the direct RIA (9.8 pg/tube) was comparable to that of the extraction RIA (10.3 p g/tube). Results for progesterone assayed in the direct RIA correlated well (r = 0.99) with the results obtained with the extraction RIA. Th e direct RIA was shown to be accurate; the mean recovery of known amou nts of progesterone added to a sample of pooled bovine plasma was 98.5 % +/- 3.29 (SEM), The direct RIA intra-assay coefficient of variation (CV) RIA for samples within the low concentration range (0.1-1.0 ng/mL ), the medium concentration range (1.0-3.0 ng/mL) and the high concent ration range (3.0-6.0 ng/mL) of progesterone were 8.1%, 8.3% and 7.73% , respectively. The inter-assay CV for plasma quality controls contain ing low (mean = 0.48 ng/mL), medium (mean = 3.0 ng/mL) and high (mean = 8.16 ng/mL) progesterone concentrations were 12.9% (n = 8), 16.9% (n = 6) and 9.72% (n = 7), respectively. In conclusion, this technique y ields a simple and rapid procedure for the measurement of progesterone in unextracted bovine plasma with no compromise in sensitivity, preci sion or accuracy.